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New Scientist Live

Mouse sperm sent into space produces healthy IVF babies

Microscopic astronauts

Alamy

By Alice Klein

We have lift-off. Freeze-dried mouse sperm that spent nine months in space has successfully impregnated female mice and created healthy offspring.

We are starting to consider space colonisation more seriously, but there are still big questions about the viability of human reproduction off Earth. The high levels of cosmic radiation and low gravity could hinder conception or lead to abnormal development of a fetus, scientists say.

Experiments have shown that fish and salamanders can reproduce normally on space stations, but research in mammals is scarce. A handful of studies in the 1980s found that male rats produced less sperm in space, but sperm quality was not assessed.

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To address this, Teruhiko Wakayama at the University of Yamanashi in Japan and his colleagues sent freeze-dried sperm from 12 male mice to the International Space Station (ISS) in August 2013. The samples were kept in a -95°C freezer for nine months, before being flown back to Earth on the SpaceX-3 carrier vehicle.

When the sperm returned, Wakayama and his team analysed its DNA. They found that it was severed in several places – most likely due to exposure to cosmic radiation. Radiation levels on the ISS are 100 times greater than levels on Earth because the station is not protected by the planet’s atmosphere and magnetic field.

However, this damage did not seem to affect fertility or offspring health. Female mice implanted with the sperm via IVF had the same birth rate as those impregnated with freeze-dried sperm that had not been exposed to space. The pups appeared healthy, and gene sequencing confirmed that they did not have any significant defects.

Female fix

The radiation damage in the DNA may have been repaired when the sperm cells were combined with the eggs to form embryos, says Andrew Wyrobek at Lawrence Berkeley National Laboratory in California. Mammalian eggs are known to have a strong capacity for repairing damaged DNA, he says. “Essentially, the female fixes up the male’s mess.”

To test the effects of space radiation not just on sperm, but sperm-egg pairings, Wakayama’s team has now received approval to send frozen mouse embryos to the ISS. There, astronauts will thaw and culture them until they reach maturity. Then they will be returned to Earth and implanted in female mice to see if they produce healthy offspring.

This experiment will also help to probe the effects of low gravity on early embryo viability. Previous studies have found that mouse and zebrafish embryos do not develop properly in simulated microgravity environments on Earth. This suggests that even if embryos can successfully form in high-radiation space environments, their growth may be hampered by the reduced gravity.

However, we won’t know for sure without experiments in space, says Wakayama. Eventually, he would like to test whether live mice can mate normally on the ISS, because this would give the best insights into whether humans could safely conceive in space. “Nobody has tried it and we really want to know.”